Brandon Nimmo froze at home plate and uncorked a well-earned fist pump. Nimmo had just rounded the bases with a go-ahead home run against former teammate Zack Wheeler, delivering one of the biggest hits yet in a Mets season filled with clutch theatrics. The sixth-inning solo shot put the Mets ahead, 2-1, over the Phillies, energizing a sold-out Citi Field crowd of 43,139 that provided a playoff-like atmosphere. That proved to be the final score in a Mets win with significant postseason ramifications. “I’m just glad that I’m contributing,” said Nimmo, who is hitting .194 since the All-Star break but had six RBI in the four-game series against the Phillies. “It’s no secret that the second half has been tougher for me, and to be able to help these guys down the stretch is just all I want to do.” With the victory, the Mets (87-69) moved into a tie with the Diamondbacks for the second National League Wild Card spot, while maintaining their two-game lead over the Braves for the final Wild Card position. The Mets and Braves begin a potentially pivotal three-game series in Atlanta on Tuesday night. The Mets took three of four from the first-place Phillies, preventing their rival from clinching the NL East at Citi Field. Sunday’s win required some heavy lifting. Wheeler, a former top Mets prospect who spent 2013-19 with the team, entered the game with a 16-6 record and a 2.56 ERA, positioning him for his third top-six finish in NL Cy Young voting in four years. Tyrone Taylor’s second-inning RBI single was the only offense the Mets managed against the ace before Nimmo’s blast barely cleared the right-field wall. The hard-throwing Wheeler held the Mets to two earned runs over seven-plus innings, striking out eight. But those two runs were enough for the Mets, who deployed four pitchers to limit the Phillies’ loaded lineup. Equipped with an overpowering fastball, Mets starter Tylor Megill allowed one run over four innings and struck out six. He boasts a 1.78 ERA in five starts since being recalled from Triple-A Syracuse on Aug. 30 to replace the injured Paul Blackburn. Phil Maton then pitched two scoreless innings in relief, and Jose Butto hurled another before closer Edwin Diaz nailed down a tense six-out save. “When I made the decision to go to him in the eighth, I wanted my best guy against their best hitters, and then let it play out,” manager Carlos Mendoza said of Diaz, who faced the top of the Phillies’ lineup in the eighth. “Once he got through that eighth with 11 pitches, that’s when I was like, I’m probably gonna send him back out.” It was the second two-inning outing of the season for Diaz, who missed all of last year with a torn patellar tendon. “We’ve been protecting him the whole year, and now it’s big-boy time,” Mendoza said. “He’s our guy. Proud of him.” Diaz stranded a runner at third base in the eighth and ninth innings. The ninth was particularly dramatic, with the Phillies putting runners on second and third with two outs, but Diaz struck out a swinging Kody Clemens with a 98.3 mph fastball to finish off the game. Saturday’s 6-3 victory over the Phillies featured some of the same heroes, with Nimmo’s seventh-inning RBI single proving to be the game-winner and Diaz getting the final four outs. Diaz expects to be available Tuesday against the Braves. “These are playoff games,” said Diaz, who totaled 47 pitches on Saturday and Sunday. “We have been playing playoff games since early September. You’ve got to be ready every single day.” Sunday marked the Mets’ last home game of the regular season. They went 6-1 on their final home stand, despite being without star shortstop Francisco Lindor, who missed his seventh consecutive game Sunday with lower-back discomfort. Adding to the scene was the attention surrounding Pete Alonso, an impending free agent who was possibly playing his final home game in a Mets uniform. Alonso received a standing ovation during his first-inning at-bat, which he acknowledged by raising his helmet to the cheering crowd. Chants of “Pete A-lon-so” filled the air during each of Alonso’s at-bats. He finished 0-for-4 with three strikeouts but came away with a lasting memory. “It was really special,” Alonso said. “It’s right out of a storybook for me. It is truly, truly remarkable to be able to see and feel that reaction and appreciation from a packed house like that.” The Mets are off Monday before beginning a six-game road trip to end the regular season. With two wins in Atlanta, the Mets would clinch a playoff spot. “The job’s not done,” Nimmo said. “There’s just as much pressure on the next game as there was on this one. You have to trust the work that we’ve put in.”